This invention relates to soles for an article of footwear, specifically to an improved exercise-providing sole for an article of footwear.
The discussion below is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present invention.
Jumping, running, plyometric exercise and power walking have grown in popularity over the last few years. Footwear and overshoes have been designed to improve muscle conditioning during these movements by increasing the angle through which the ankle flexes. This works the calf muscles through a more full range of motion than is possible in traditional footwear. The effect is achieved by placing the vertically thickest section of the sole forward of the heel.
Some soles have been designed providing a rocker structure with an elevated heel. Examples of this include Famolare, U.S. Pat. No. 3,936,956, Daswick, U.S. Pat. No. 4,241,523 and Spronken, U.S. Pat. No. 4,425,721.
Some references describe a sole with a thicker section forward of the heel without a rocker structure. This structure has been associated with a forefoot to ground slapping motion which may cause injury to the wearer. Examples of this include Monier, U.S. Pat. No. 2,769,252, Cox, U.S. Pat. No. 3,739,500 and Nakamoto, U.S. Pat. No. 3,859,727.
Other structure are described in which the thickest vertical section of the sole is behind the metatarsal heads. Examples of this structure include Newell, U.S. Pat. No. 3,602,424, Phillips, U.S. Pat. No. 4,155,180 and Bunke, U.S. Pat. No. 4,811,504.
Other structures are descried that place a vertically thickest sole section forward of the distal metatarsal joints of a wearer's foot. Examples of this include Wenker, U.S. Pat. No. 2,172,000 and Baker, U.S. Pat. No. 3,472,508.
A number of alternative radii and alignments of sole structure have been described. For example, Kalsoy, U.S. Pat. No. 3,305,947 describes a sole structure having a curved bottom to transfer weight from the outer portion of the heel to the big toe during a step, Banister, U.S. Pat. No. 2,283,595 describes a stilt structure attachable to shoes which has a compound curve on the lower surface, Witherill, U.S. Pat. No. 2,328,242 describes a sole structure which has generally the contours of a human foot, and Urban, U.S. Pat. No. 2,519,613 describes a protective device which is attachable to a shoe sole and which prevents contact of the toe of the shoe with the ground during normal walking.